The Fascinating Reason Why Temperature Has No Upper Limit?

Temperature has no upper limit, yet a fixed lower limit. To elaborate, the lowest temperature possible is 0 K (zero Kelvin) or -273.15°C (degrees Celsius).

On the other hand, we do not know what the highest temperature possible could be, meaning we do not know temperature’s upper limit.

What about temperature makes it impossible for it to go below 0 K? And what about it makes the upper limit currently unknown to us? Those are the fascinating questions I am trying to address with this article.

I will be tackling these questions by solving the following 5 incremental puzzles:

1. How do we measure temperature?

2. What exactly is temperature?

3. Why does temperature have a lower limit?

4. Temperature has no upper limit!

5. What remains unknown to us about temperature?

As I solve each puzzle, the mystery will gradually unravel itself to you. On your part, you don’t need any deep knowledge about any of this stuff beforehand. I will be using simple language as much as possible so that anyone who reads can just ‘get it’.

If you are as curious and excited as I am, let’s jump right into it!

This essay is supported by Generatebg

How is Temperature Measured?

Part of our fascination about temperature in this article comes from its fixed lower limit. It is fixed at -273.15°C or 0 K. Here, -273.15°C can look like a random number.

It’s because Celsius was a measuring scale (unit system) that was invented with water and its phase change as the basis. 0°C is the freezing point of water, and 100°C is its boiling point (both at 1 atmospheric pressure; I’ll get into pressure’s relevance later).

Hence, when we generalize the Celsius unit system’s use, it leads to a random-looking number for the absolute lowest temperature.

To overcome this seeming confusion, Kelvin is used often in the scientific world. In the Kelvin unit system, the lowest possible temperature is clearly defined by zero – a concept that makes intuitive mathematical sense to anyone who reads the number.

Apart from the starting point, there exists not much difference between the Kelvin unit system and the Celsius unit system. The temperature difference of one degree Celsius and that of one Kelvin are exactly the same.

Now that we’ve solved the first puzzle, it’s time we moved on to the next one.

What Exactly is Temperature?

When you ponder upon this question, you might answer:

“Temperature is how hot or cold something is.”

or something along those lines. But if I were to further question what does ‘hot’ or ‘cold’ mean, we would start to arrive at the root of our question.

Hotness or coldness is a way of measuring the state of energy of an object (or matter, more generally speaking). To simplify further, temperature is used to measure the amount of active (kinetic) energy within a body.

When a body heats up, its particles start to move about. For ease of understanding, let’s visualize the particles to be vibrating. The more or faster the particles vibrate, the hotter the body gets. The lesser or slower the particles vibrate, the colder the body gets.

When the vibration gets out of control (in either direction), phase change results. This is when water vaporizes or freezes due to heat or cold, for instance.

As far as we are concerned, temperature measures how fast or slow the particles within a body are vibrating. Right, onward to our next puzzle we go!

Why Does Temperature Have a Lower Limit?

We know that as temperature drops, the particles within a body vibrate lesser and lesser. Let’s assume that the temperature keeps dropping further.

At some critical point, the vibration of the particles simply stops. The particles just freeze! This means that the particles cannot vibrate any slower than this.

Regardless of the nature of the matter involved, the particles stop vibrating when they reach a temperature of -273.15°C or 0 K. This is the coldest anything can get. That’s why temperature has a lower limit.

Over the years, scientists argued that there have been recorded cases of sub-zero Kelvin temperatures. But recent research has proven these reports wrong, terming them as errors due to mathematical and thermodynamic inconsistencies:

“Here, we prove that all previous negative temperature claims and their implications are invalid as they arise from the use of an entropy definition that is inconsistent both mathematically and thermodynamically.”

– Jörn Dunkel and Stefan Hilbert in Nature Physics (scientific research publication).

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Temperature has no upper limit!

Now that we’ve solved the lower limit puzzle, it’s time for the upper limit puzzle.

We know that if we keep heating something, the particles keep vibrating faster and faster. So, what happens if we just keep on heating something?

At some point, the particles vibrate so fast that the molecules come apart. This leads to the phase change we talked about earlier. When molecules start coming apart, solids start melting and then vaporizing.

But what if we keep heating matter beyond this point? Molecules and atoms start separating due to increased vibration, and something called plasma is formed. At this point, we reach temperatures akin to those experienced on the surface of the sun.

You can start to grasp the challenge we are facing here. We could keep heating things further, but we simply do not know how yet. The reason is that we haven’t fully understood the nature of our universe, which brings us promptly to our last puzzle.

What Remains Unknown to Us About Temperature?

Do you remember that I said something about pressure earlier? Yes, physical properties such as pressure and density affect the temperature.

For example, water’s boiling point can be changed by changing the environmental pressure. This is why I mentioned a specific pressure number for the boiling point and freezing point of water.

When we continue heating substances, it also affects the pressure and density. We have an understanding of how these quantities are related only until a certain point.

We get this understanding from observing stars such as the sun. Stars are large burning gas-balls after all.

There is some scientific reasoning towards thinking that extremely high temperatures might distort space-time itself. But at this point, we are talking about temperatures many orders of magnitude higher than anything we see in the cosmos.

Such temperatures would have been experienced during the big bang. We have no clear understanding if the temperature can be raised further if space-time does not exist anymore. Is it even fair to call it ‘temperature’ at that point?

Time To Take It Easy!

If all this sounds very confusing to you, rest assured that nobody understands temperature beyond a certain point anyway.

I did try to solve the final puzzle to the best of my ability. But if you are wondering why temperature behaves this way, I must humbly admit that I (unfortunately) did not design our universe. So, we have to draw the line there and call it a day, whilst being thankful for knowing what we can know!

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Further reading that might interest you: Can You Unplug Your USB Stick When You Want? and What Really Happens To Your Knees When You Gain 1 Kg.